ACJC 2022 Prelim P3 QP

3 © ACJC2022 9729/03/Prelim/2022 [Turn over Section A Answer all the questions in this section. 1 (a) Explain what is meant by the term Lewis acid. [1] …………………………………………………………………………………………………… ………………………………………………………………………………………….............. …………………………………………………………………………………………………… (b) The water molecule can react in various ways: as an acid, as a base, as a nucleophile, as an oxidising agent and as a reducing agent. Study the following reactions and decide in which way water is reacting in each case. Explain your answers fully. (i) 2F2 + 2H2O → 4HF + O2 [1] (ii) CH3COCl + H2O → CH3COOH + HCl [1] (iii) H2PO4− + H2O HPO42− + H3O+ [1] (iv) Li + H2O → LiOH + ½H2 [1] (v) NO2− + H2O HNO2 + OH− [1] …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. ……………………………………………………………………………………………..

4 © ACJC 2022 9729/03/Prelim/2022 [Turn over …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. (c) The pKa values of three acids are listed in Table 1.1. Table 1.1 acid formula pKa 1 CH3CH2COOH 4.9 2 CH3CHClCOOH 2.8 3 CH2ClCH2COOH z (i) Explain the difference in pKa values between acid 1 and acid 2. [2] (ii) Suggest a value for z and explain your answer. [1] (iii) Peroxyacids are weak acids. One way to prepare peroxypropanoic acid is to treat the corresponding carboxylic acid with hydrogen peroxide. acid 1 peroxypropano